1. Field of the Invention
The invention relates to a semi-conductor mounting apparatus for applying adhesive to a substrate in the area of a chip mounting surface.
2. The Background Art
The widespread practice of mounting semiconductor chips using adhesive (usually epoxy-based) assumes a metered application of the adhesive in a certain distribution on the mounting surface so that when the chip is subsequently applied, there is a layer of adhesive spread as evenly as possible over the entire surface of the chip, free from trapped air. In order to obtain this, different "figurative" patterns of application are used, ranging from a simple diagonal cross to line patterns with a plurality of branches, according to the format of the chip, type of adhesive and further parameters.
Within an automated mounting mechanism, known as a "die bonder", a particular apparatus is used for the application of adhesive. This apparatus moves a dispenser over the substrate. The desired pattern of application can thus be produced in different ways. For example, a die-type dispensing tool may be used, which has a large number of nozzles arranged in rows corresponding to the pattern (a "multitube dispenser"). Such tools must be individually manufactured and changed for each pattern. Another application apparatus that may be used has a single nozzle, which is guided over the substrate in a programmed movement corresponding to the pattern and thus "draws" the pattern of lines (a "programmable dispenser"). A considerable advantage of this apparatus is in that any pattern can be produced using the same, relatively simple tool, simply by amending the software. Nevertheless, it is necessary to carry out the programmed movements with sufficient precision, and above all at high speed, so that even branched patterns can be "drawn" with short cycle times.
Known apparatus of the type described above have the following features:
an adhesive dispensing head moveable in three coordinate dimensions (x, y, z) PA1 a first carriage which is moveable in two dimensions (x, y) parallel to the mounting surface using associated first and second actuators, and PA1 a second carriage which is moveable on a guide connected to the first carriage, in the third dimension (z) perpendicular to the mounting surface using a third actuator, and which carries the dispensing head.
One of the known embodiments is a "standard" three-axis control unit with three overlying carriages, each provided with an actuator, and in another case although the x and y actuators of the first carriage are not coupled together, the third (z) actuator together with its carriage is mounted on the first x/y carriage and is moved along with it. With such apparatus according to the prior art, it is difficult to obtain the required mechanical stability and precision of control over the whole three-axis working surface. Above all, however, the acceleration and speeds of the controlling movements obtainable are limited because the weight of powerful positioning motors in turn requires correspondingly stable carriage guides, which as a whole results in ever greater masses being moved.
The object of the invention is to overcome the disadvantages and limitations of the prior art, and to improve the dynamic properties of such apparatus in order to obtain faster accelerations and control speeds of the dispensing head and thereby shorter cycle times for "drawing" the pattern of adhesive.